Furthermore, the invention relates to a method for producing such a casing for an aircraft engine, whereby several prepreg plies in which fibers are oriented differently are arranged and hardened on a mold.
For reducing the weight of aircraft components also casings of aircraft engines, in particular bypass pipes or so-called fan casings are increasingly made of fiber-reinforced plastics. Usually the casing is made of several prepreg plies, whereby the individual prepreg plies are again made of several, usually 3 to 4 segments arranged in the peripheral direction of the casing in an overlapping manner. To improve the bending and torsional strengths, the orientation of the fibers of the individual prepreg plies is selected with different angles, in particular 0° and 90° for the bending load and +/−45° for the torsional load.
In particular, bypass pipes which form the outer boundary of the so-called bypass duct, the annular gap around the engine, and fan casings, that is cylinder-shaped casings of the propeller of the engine are produced as casings for aircraft engines.
For example, EP 1 646 776 B1 describes an aircraft engine comprising such a bypass casing.
The US 2013/0216367 A1 relates to a fan casing for an aircraft engine consisting of windings made of threads and non-crimp fabrics, the main focus being directed to the strength in the case of breaking of the propeller of the engine, whereas no fire resistance is described.
What is of disadvantage in such casings is the relatively high waste of prepreg materials, in particular in an orientation of the fibers in the range of +/−45°, since the raw materials for the prepregs are usually available on continuous reels having longitudinally extending fibers. In addition, the lack of uninterrupted fibers extending about the entire circumference of the casing will lead to a loss of strength, which in particular in fire resistance tests required in the aircraft industry may result in the dissolution of the plies and in a rejection of the component.
As a matter of fact, the disadvantage with respect to the strength may be improved by reducing the amount of segments per prepreg ply and at best by increasing the overlapping portion, however, the disadvantage of a large quantity of waste, in particular in the case of transversely extending fibers continues to exist and will result in increased production costs.
It is the object of the present invention to provide an above casing for an aircraft engine and a method for producing such a casing, by which the strength properties can be improved and production costs be reduced. Disadvantages of known casings or methods for producing such casings are to be avoided or at least reduced.
The object is achieved by a casing cited above, wherein at least one reinforcement ply is provided that consists of a prepreg strip having several windings, and the prepreg strip of each reinforcement ply includes a lateral overlapping portion. By the additional arrangement of such reinforcement plies formed by a prepreg strip, which can be arranged in several windings to form the casing, the strength of the casing can be increased essentially. Furthermore, prepreg plies having a transverse fiber orientation, which result in a high amount of waste, can be prevented by arranging the prepreg strips of each reinforcement ply accordingly. Thus, the production costs can be reduced, without reducing the strength properties of the casing. The fibers of the prepreg strip of each reinforcement ply are available across the at least one winding, preferably without interruption. The strength of the casing can be increased further by the lateral overlapping of the prepreg strip. In particular, a delamination in fire resistance tests can be prevented effectively or at least be complicated.
According to a further feature of the invention the prepreg strip of each reinforcement ply has a length corresponding to at least the periphery of the casing to be formed and a width corresponding to a fraction of the length of the casing. Thus, the reinforcement ply of the casing is produced by a prepreg strip which is wound around several times. Depending on the width of the prepreg strip and the overlapping of the prepreg strip from one winding to the next winding the prepreg strip has to be wound around the previous prepreg ply or the respective base often enough.
The windings of the prepreg strip of each reinforcement ply may have a constant pitch angle. The result of such an essentially constant pitch angle will be a corresponding inclination of the fibers present in the prepreg strip (usually available in the longitudinal direction of the prepreg strip), whereby the torsional strength of the casing can be increased, without having to use prepregs with a transverse fiber direction.
Alternatively, the windings of the prepreg strip of each reinforcement ply may also have a constant pitch. Instead of a constant pitch angle described above, the winding of a prepreg strip of each reinforcement ply may also extend essentially straight and be deflected or displaced only to form the next winding essentially by a width of the prepreg strip, which will be repeated as often as desired in each winding of the prepreg strip. It is important in this connection that at least the majority of the fibers of the prepreg strip are present across at least one winding without interruption.
The windings of the prepreg strip of each reinforcement ply may be arranged crosswise. An especially high torsional strength is achieved by such a crosswise arrangement of the windings of the prepreg strip of a reinforcement ply. Nevertheless, a prepreg strip with longitudinally extending fibers can be used with or without essential waste.
If the fibers of at least one prepreg ply and of at least one reinforcement ply have an orientation of essentially 0° or 90°, the waste can be minimized correspondingly. Using the majority or prepreg plies and prepreg strips with such an orientation of the fibers or minor deviations thereof will result in a very low amount of waste. The required torsional strength is achieved additionally by a transverse course of the prepreg strips of each reinforcement ply.
Each prepreg ply preferably consists of several, preferably 3 or 4 segments having a width which essentially corresponds to the length of the casing, and the segments are arranged with an overlapping portion in the peripheral direction of the casing. This construction known per se is now combined with at least one reinforcement ply, at best several reinforcement plies comprising prepreg strips correspondingly wrapped around, whereby an increase in strength can be achieved.
The fibers may be made of carbon fibers and/or glass fibers and/or aramide fibers and/or ceramic fibers. The type of reinforcement fibers used and their orientation are adapted to the respective applications and requirements.
The object is also achieved by a method of production mentioned above, wherein in addition to the prepreg plies at least one reinforcement ply made of a prepreg strip arranged in several windings is arranged on the mold prior to hardening, whereby the prepreg strip of each reinforcement ply is arranged with a lateral overlapping portion. As mentioned above, the strength of the casing can be increased by using such a reinforcement ply and the production costs can be reduced by reducing the waste of the prepreg materials. Concerning the other advantages reference is made to the above description of the casing.
The prepreg strip of each reinforcement ply can be arranged with an essentially constant pitch angle or a continuous pitch.
If the windings of the prepreg strip of each reinforcement ply are arranged crosswise, in particular an increase in the torsional strength can be achieved.
Preferably, at least one prepreg ply and at least one reinforcement ply are used, in which the fibers are oriented at essentially 0° and 90°, respectively. As mentioned above, this can reduce the waste and thus the production costs.
For forming each prepreg ply several, preferably 3 or 4 segments having a width, which corresponds to the length of the casing, are arranged with an overlapping portion in the peripheral direction of the casing.
Preferably, prepreg plies and reinforcement plies having fibers made of carbon and/or glass and/or aramide and/or ceramics are used.